1. Field of the Invention
This invention relates to a working machine for trial construction of a printed circuit board (hereinafter called a PCB) by effecting some kinds of working, such as making a circuit pattern on a copper-foiled substrate, making holes in lands, and so on, in accordance with geometrical data made by a CAD.
2. Description of the Prior Art
In order to develop electronic devices and to fabricate such devices that are small in amount of production and hence not suitable for mass production, there is an increasing need for constructing PCB substrates with appropriate electronic circuits on a trial basis, precisely, quickly, and at a low cost,.
However, since trial construction of PCBs needs steps of photographic, chemical, and other treatments, circuit patterns must be made even for fabricating a small amount of trial PCBs, and most of planners, designers and other engineers have been compelled to order such work to specialists.
In order to improve the situation, there has been proposed a PCB working machine for making a circuit pattern by cutting a copper-foiled substrate in which a copper layer is provided on an insulating substrate.
More specifically, such PCB working machines are configured such that a cutting tool is fixed to a spindle moveable in X-axis and Y-axis directions under a control, and it is moved, in accordance with a predetermined pattern, on a PCB substrate which is held in place on a work table with a suction force, to cut the copper layer and the insulating substrate on the PCB substrate to make a target circuit.
In the PCB working machines referred to above, the cutting tool has, at its distal end, a pyramid-shaped cutting edge with a 90 degrees apex, for example, and the cutting tool is fixed to a chuck provided at a distal end of a spindle. Thus the cutting tool is rotated and moved down by a controlled amount onto a PCB substrate by a stepping motor, and then moved in X-axis and Y-axis directions to cut the surface of the PCB substrate into a circuit board having a desired pattern.
In the working machines having the foregoing construction, after the cutting tool is fixed to the chuck at the distal end of the spindle, the cutting edge of the cutting tool is brought into contact with the surface of the PCB substrate to detect the position of the surface of the PCB substrate. After that, the spindle is driven to move down by a necessary amount by a stepping motor for Z-axis movements such that the cutting edge of the cutting tool cuts into the surface of the PCB substrate by-a precise depth. That is, the widths of cuts are controlled in the foregoing process.
This method, however, is likely to cause errors in level of the cutting edge of the cutting tool relative to the level of the surface of the PCB substrate, because of a microscopic unevenness of the surface of the PCB substrate or displacement of the spindle caused by heat. In case of a 90.degree.-angled cutting edge, the error in width of a cut will be as large as twice an error in level of the cutting edge (Z-axis direction). This is a serious problem in making a circuit pattern with microscopically distant lines.
The aforementioned method also involves a problem such that shavings may remain on the worked surface. Such shavings, if remaining on the worked surface, may cause a short-circuit between lines or cut and break the circuit pattern.
Cutting tools are subject to breakage. When such breakage occurs during automatic driving of the machine, it results in defective cuts.
Moreover, in the working machines having the above-described construction, the cutting tool is likely to stick to the chuck, and it has been difficult to automate replacement of the tool with another. Therefore, unmanned driving of such machines during night has been difficult.